Part 1 : How to apply for a K-1 fiance(e) visa of a U.S. citizen

The fiancé(e) K-1 nonimmigrant visa is for the foreign-citizen fiancé(e) of a United States (U.S.) citizen. The K-1 visa permits the foreign-citizen fiancé(e) to travel to the United States and marry his or her U.S. citizen sponsor within 90 days of arrival. The foreign-citizen will then apply for adjustment of status to a permanent resident (LPR) with the Department of Homeland Security’s (DHS) U.S. Citizenship and Immigration Services (USCIS). Because a fiancé(e) visa permits the holder to immigrate to the U.S. and marry a U.S. citizen shortly after arrival in the United States, the fiancé(e) must meet some of the requirements of an immigrant visa. Eligible children of K-1 visa applicants receive K-2 visas.

What Is a “Fiancé(e)”?

Under U.S. immigration law, a foreign-citizen fiancé(e) of a U.S. citizen is the recipient of an approved Petition for Alien Fiancé(e), Form I-129F, who has been issued a nonimmigrant K-1 visa for travel to the United States in order to marry his or her U.S. citizen fiancé(e). Both the U.S. citizen and the K-1 visa applicant must have been legally free to marry at the time the petition was filed and must have remained so thereafter.

The marriage must be legally possible according to laws of the U.S. state in which the marriage will take place.
In general, the foreign-citizen fiancé(e) and U.S. citizen sponsor must have met in person within the past two years. USCIS may grant an exception to this requirement, based on extreme hardship for the U.S. citizen sponsor to personally meet the foreign-citizen fiancé(e), or, for example, if it is contrary in the U.S. citizen sponsor’s or foreign-citizen fiancé(e)’s culture for a man and woman to meet before marriage.

http://travel.state.gov/visa/immigrants/types/types_2994.html

Steps to Bringing your Fiance to the US through the K-1 Visa

Step 1:
File a petition with the USCIS on behalf of your Fiance
You, the US citizen, must file the Petition for Alien fiance (Form I-129F) with your local U.S. Citizenship and Immigration Services (USCIS) office.

Step 2:
The Fiance's obtains a visa at a US consulate at his/her home country
After the USCIS approves the petition, it sends the petition to the embassy or consulate where your fiance will apply for a K-1 non-immigrant visa. Once approved he/she will get a visa stamped on their passport and will be ready to come to the United States.

Once you've received the K-1 Visa successfully you are ready to enter the United States. Following are some important information and steps for you and your fiance to follow through on after entering the United States.

Step 3:
Entering into the United States
After getting the fiance visa, your fiance enters the United States through a U.S. immigration port-of-entry. The U.S. immigration official gives your fiance instructions on what to do at the the port of entry.

Step 4:
Get Social Security Number
Your fiance can apply for a social security number card. There are many advantages of having a social security number card the sooner the better.
A permanent resident of the United States needs a Social Security number to:
Work in the United States
Conduct business with a bank or financial institution
Pay taxes or to be claimed on a tax return
And for other purposes not listed.
Refer to the Social Security Website for further instructions

Step 5:
Get Married
As per the condition of the K-1 Visa you and your fiance must get married within 90 days of his/her arrival.

Step 6:
Apply for Permanent Residency (Green Card) by Filing Adjustment of Status (AOS/I-485)
If your spouse plans to work and stay in the US, after marriage, he/she must file Form I-485 Application to register as permanent residence or to adjust status with the USCIS office that serves the area where you live in the United States. You must fill out the Affidavit of Support, Form I-864, with the USCIS for your spouse's application to become a lawful permanent resident (LPR).

Step 7:
Remove Conditions on Permanent Status for Your New Spouse
The permanent residence you have received through this marriage is conditional, which means your new spouse's green card will expire in 2 years. You'll have to file the I-751 petition in order to remove this conditional status.
Find Out More On Petition to Remove the Conditions on Residence
Download I-751 Form - Petition to Remove the Conditions on Residence